# Peptide Mundo — Metabolic & Weight Research Peptides > Peptide Mundo is a reference desk for metabolic and weight research peptides — semaglutide, tirzepatide, and retatrutide — summarized from peer-reviewed literature across the incretin agonism spectrum. A digest, not a vendor or clinic. A measured reading desk for the published science on semaglutide, tirzepatide, and retatrutide — what each receptor arm does, how the trials compare, and how far the evidence actually reaches. ## The short version Peptide Mundo is a reading desk, not a store. It collects what the published research literature actually says about three peptides that have reshaped how scientists and clinicians think about **metabolic regulation and weight management**: semaglutide, tirzepatide, and retatrutide. Each is an *incretin mimetic* — a synthetic peptide that mimics hormones the gut releases after a meal to signal fullness, regulate blood sugar, and (in some cases) increase energy expenditure. The organizing question here is **how many receptor arms a molecule engages**. Semaglutide activates one — the GLP-1 receptor. Tirzepatide activates two (GLP-1 and GIP). Retatrutide activates three (GLP-1, GIP, and glucagon). Each additional receptor arm adds something to the metabolic picture, and the clinical trial numbers tell a broadly consistent story: more receptor engagement has so far meant more weight lost. This desk does one job: it tells you, in plain language and with citations, what each peptide was tested on, in which populations, and how far that evidence really reaches. We do not sell anything, we do not give medical advice, and we never list a human dose outside the context of a cited study. ## What are research peptides? Peptides are short chains of amino acids — the same building blocks that make up proteins, only far smaller. The compounds on this desk are *incretin-class* peptides: synthetic analogues of hormones (GLP-1, GIP, and glucagon) that the intestine releases in response to food. Because they are structurally similar to those natural hormones, they activate the same receptors, but they have been chemically modified — through backbone substitutions and fatty-acid side chains — to resist breakdown and allow once-weekly dosing. Semaglutide and tirzepatide are *approved prescription medicines* for specific indications in adults. Retatrutide is *investigational*: it is in Phase 3 clinical trials and is not approved by the FDA or any regulator as of 2026. Research-grade material described by suppliers as being for laboratory use only falls outside the approved-product evidence base and carries documented quality and safety concerns. Whenever this site reports a dosing number, it reports it exactly as the study did — never as a recommendation. ## How these three fit into incretin research The three peptides on this desk form a progression across the incretin agonism spectrum, which is exactly why they sit together. - [**Semaglutide**](/semaglutide) is the baseline. A GLP-1 receptor agonist, it was the first agent in this class to demonstrate large-scale weight loss alongside cardiovascular and kidney benefits in landmark trials [2][3][4]. Its approval across type 2 diabetes, chronic weight management, cardiovascular risk reduction, and (in 2025) metabolic liver disease makes it the benchmark all newer agents are measured against [1]. - [**Tirzepatide**](/tirzepatide) is the lead on this desk. By adding GIP receptor activation alongside GLP-1, it became the first approved dual incretin agonist and, in the head-to-head SURMOUNT-5 trial, produced significantly greater weight loss than semaglutide (-20.2% versus -13.7%) over 72 weeks [1]. It is FDA-approved for type 2 diabetes, chronic weight management, and sleep apnea. - [**Retatrutide**](/retatrutide) is the frontier. Adding glucagon receptor agonism to the GIP/GLP-1 combination is proposed to increase energy expenditure — the thermogenic component — alongside appetite suppression, and Phase 2 data showed up to -24.2% body weight at 48 weeks [15]. Phase 3 trials (TRIUMPH) are ongoing; no approval exists yet. Together they sketch a mechanistic ladder — one arm, two arms, three arms — that illuminates what each incretin receptor contributes. Use the individual pages to read each one, or [compare these peptides](/compare) side by side. ## A note on how this desk reads the literature Peptide Mundo is a cross-referenced literature digest. Each peptide page summarizes the peer-reviewed studies for that compound, cites them by number, and links to a single shared [references list](/references) that aggregates every source across all three. Semaglutide and tirzepatide carry large, well-funded clinical trial programs with sponsor involvement — that is the standard for novel prescription drugs, and this desk notes it where it is relevant to weighing the evidence. Retatrutide's evidence is Phase 2 only; the desk says so plainly and does not extrapolate beyond what was studied. Where safety signals exist — gastrointestinal intolerance, gallbladder risk, lean-mass loss, or an investigational classification — they appear in the text, not in footnotes. The aim is a disciplined, accurate account of what is known and how confidently it is known, so a reader can calibrate their own understanding rather than simply absorbing a conclusion. --- A peer-reviewed literature digest on incretin-class metabolic peptides — citations and context, not clinical counsel.